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Metabolic Flexibility, Intermittent Fasting and the New England Journal of Medicine (part 2) – Equip For Health


Read part 1 here

How do I become metabolically flexible? 

  • Eating  
  • Exercising  
  • Not eating (keep reading and I’ll explain) 

I will briefly summarize some of the important aspect of developing metabolic flexibility.  If you have been consuming a SAD diet for years, please understand that this transition will take time!  For some it might be a week or two and others it might be three or four weeks.  If you already eat healthy and are lean, you might already be metabolically flexible and not even know it! 

Eating the right foods 

Firstly, eliminate processed foods and refined carbs.  Get rid of the bagels, pastries, breakfast cereals, breads, pastas, fruit juices, soft drinks, candy, energy drinks, syrups and anything with sugar.  These are nutrient void foods that will only make the blood sugar roller coaster keep rolling and keep your glycogen stores full, rendering you unable to burn bodyfat. 

Focus on whole food nutrition.  Basically, eat real food!  Lots of veggies, healthy, responsibly sourced animal products, healthy fats (such as extra virgin olive and avocado based products), some nuts and seeds as well as select fruits and occasional starchy tubers (potatoes, sweet potatoes)  These will be low-glycemic and full of nutrition, keeping you satiated and allowing longer periods of time between meals. 

By eating whole foods you will, by default, be eating less carbs, especially the high-glycemic carbs, so you will be more likely to keep glycogen levels lower (stored carbs in the muscles) giving you a better chance at tapping into bodyfat for fuel.   


Exercising on a regular basis will also help you to tap into your bodyfat stores.  I’m not going into great detail here, but a regular exercise regimen that includes both strength and cardiovascular training is ideal.  In addition, keep busy on your feet and try to hit 10,000 steps a day—there is nothing magical about this number, it just means you’ve been active and on your feet!  Exercise, especially full body strength training, is an AMAZING way to deplete glycogen stores.   

Intermittent fasting (IF) 

Intermittent fasting.  Time restricted eating. 5:2 fasting.  Multi-day fasting fasting.  There are lots and lots of intermittent fasting variations.  There is really no agreed upon definition what actually constitutes IF, but there are a few IF strategies that are generally recognized as safe and effective from various studies as well as many, many anecdotes.  There are some fasting zealots out there who think that a true “intermittent fast” is fasting for 24 hours or longer—there are people out there doing regular 3 day to 7-day (and even more) water only fasts! (we do NOT recommend this without medical supervision!). 

The idea of IF is to go a long period of time without eating.  Long enough, in most cases, to where your body switches from glucose (carb) burning to fat (or ketone) burning (which happens when you deplete your glycogen stores).  This can differ depending on the person, fasting the protocol and various other factors.  What happens when you go without eating for an extended period of time on a regular basis is truly quite remarkable! (I will get into this later).   

Our recommendation for IF for the average person is time-restricted feeding.  Although we personally don’t practice this, 5:2 fasting is another reasonable, sustainable alternative.   

Time-restricted feeding (TRF) is limiting the consumption of any calories (from food or beverage) into what is called a “feeding window”.  This follows, or is followed by (depending on your perspective) a fasting window.   

5:2 fasting is picking 2 days each week in which you “fast” by eating very low calories, somewhere in the neighborhood of 500-700 calories for the entire day.  

What is the correct length to fast/feed on a time-restricted feeding plan? 

Well, it depends.  

There are so many factors that play into this I cannot possible break all of these down in this one discussion.  We are all unique individuals at different stages of life, different ages, different stress levels and different body types.  None of this can be generalized.  In fact, it usually takes some degree of self-experimentation or following along with people who can help sensibly guide you in the process (insert shameless plug here for Sustain). 

If you are currently on the SAD diet, eating/snacking all the time and not fasting other than when you sleep, then clean your diet up first and foremost.   After you adjust to your new eating plan you can start thinking about incorporating some intermittent fasting into your lifestyle.  At Equip for Health, our opinion is TRF is the most lifestyle friendly, effective and habit-forming practice of IF for most every day, average Joes and Janes.  I’m not going to give all the tips and secrets away!. (If you want to get started on this process check out our program, Sustain, which will walk you through getting started on TRF and healthy living

Intermittent Fasting is so amazing, in fact, there was a recent publication in the prestigious New England Journal of Medicine discussing this topic in further detail, which I will briefly summarize below.  

For those of you who have been following Molly and me for any length of time, it is no secret we are fond of IF and have been preaching its attributes for quite some time now.   We are not alone in our sentiments regarding IF!  Not only are many health zealots and biohackers shouting from the rooftops about the amazing benefits of IF, there are many, many medical doctors and PhD researchers also shouting from the rooftops about the benefits of IF.  Animal and human research has been going on for quite some time now studying the effects of IF.  There are many complex processes that take place in the body during the fasting state.  Some of these are not even completely understood!  What is important, are the benefits from regular periods of intermittent fasting. 

Here are some of the noteworthy highlights from the article about IF: 

  • Encourages metabolic switching (also known as metabolic flexibility) back and forth from glucose to ketones 
  • Elicits “adaptive cellular responses” 
  • “improves glucose regulation 
  • “increases stress resistance” 
  • “suppresses inflammation” 
  • “enhance intrinsic defenses against oxidative and metabolic stress and those that remove or repair damaged molecules” 
  • Fights disease: “obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative brain diseases” 
  • “elicits high orchestrated systemic and cellular responses that carry over into the fed state to bolster mental and physical performance, as well as disease resistance” 
  • “increased expression of antioxidant defenses, DNA repair, protein quality control, mitochondrial biogenesis and autophagy, and down-regulation of inflammation.” 
  • “ameliorate obesity, insulin resistance, dyslipidemia, hypertension, and inflammation” 
  • In certain cancers in animal models fasting, “reduces the occurrence of spontaneous tumors” 
  • “alternate-day fasting can delay the onset and progression of the disease process in animal models of Alzheimer’s disease and Parkinson’s disease” 

The article goes into great detail about the physiological effects of IF and notes various other potential benefits along with some other discussions.  Here’s the link to the NEJM article in case you want to read it yourself: 

Thanks for reading! 



Rafael de Cabo, Ph.D., and Mark P. Mattson, Ph.D., N Engl J Med 2019; 381:2541-2551 DOI: 10.1056/NEJMra1905136 

Ryan Parnham

Author Ryan Parnham

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